Thermal regenerative cracking apparatus and separation system therefor

ABSTRACT

This invention relates to an apparatus and method embodied in a TRC system for rapidly separating particulate solids from a mixed phase solids-gas stream which may be at velocities up to 150 ft./sec. and at high temperature. Specifically, the device is designed for incorporation at the discharge of solid-gas reacting TRC systems having low residence time requirements and carried out in tubular type reactors. Separation is effected by projecting solids by centrifugal force against a bed of solids as the gas phase makes a 180° directional change, said solids changing direction only 90° relative to the incoming stream.

CROSS REFERENCE TO RELATED CASE

This is a continuation-in-part application of Ser. No. 06/055,148 filedJuly 6, 1979, now U.S. Pat. No. 4,288,235.

BACKGROUND OF THE INVENTION

1. Field of The Invention

This invention relates generally to a separation system and process toobtain a primary separation of particulate solids from a mixed phasegas-solid stream in a Thermal Regenerative Cracking (TRC) apparatus andprocess described in U.S. Pat. No. 4,061,562 to McKinney et al and U.S.Pat. No. 4,097,363 to McKinney et al.

2. Description of The Prior Art

Chemical reaction systems utilizing solids in contact with a gaseous orvaporized stream have long been employed. The solids may participate inthe reaction as catalyst, provide heat required for an endothermicreaction, or both. Alternatively the solids may provide a heat sink inthe case of an exothermic reaction. Fluidized bed reactors havesubstantial advantages, most notably an isothermal temperature profile.However, as residence time decreases the fluidized bed depth becomesshallower and increasingly unstable. For this reason tubular reactorsemploying solid-gas contact in pneumatic flow have been used and withgreat success, particularly in the catalytic cracking of hydrocarbons toproduce gasolines where reaction residence times are between 2 and 5seconds.

As residence times become lower, generally below 2 seconds andspecifically below 1 second, the ability to separate the gaseousproducts from the solids is diminished because there is insufficienttime to do so effectively. This occurs because the residence timerequirements of separation means such as cyclones begin to represent adisproportionate fraction of the allowable reactor residence time. Theproblem is acute in reaction systems such as thermal cracking ofhydrocarbons to produce olefins and catalytic cracking to producegasoline using improved catalysts where the total reactor residence timeis between 0.2 and 1.0 seconds. In these reaction systems conventionalseparation devices may consume more than 35% of the allowable contacttime between the two phases resulting in product degradation, cokeformation, low yields and varying severity.

In non-catalytic, temperature dependent endothermic reactions, ratherthan separating the phases, it is possible to quench the entire productstream after the requisite reaction period. However, these solids areusually recycled and are regenerated by heating to high temperatures. Aquench of the reactor effluent prior to separation would be thermallyinefficient. However, it is economically viable to make a primaryseparation of the particulate solids before quench of the gaseousstream. The residual solids in the quenched stream may then be separatedin a conventional separator inasmuch as solids gas contact is no longera concern.

In some reaction systems, specifically catalytic reactions at low ormoderate temperatures, quench of the product gas is undesirable from aprocess standpoint. In other cases the quench is ineffective interminating the reaction. Thus, these reaction systems require immediateseparation of the phases to remove catalyst from the gas phase. Once thecatalyst has been removed, the mechanism for reaction is no longerpresent.

The prior art has attempted to separate the phases rapidly by use ofcentrifugal force or deflection means, as exemplified by U.S. Pat. No.2,737,479 to Nicholson; U.S. Pat. No. 2,878,891 to Ross; and U.S. Pat.No. 3,074,878 to Pappas.

In a TRC system having a short residence time (i.e., in the range of0.05 to 2 seconds, at temperatures in the range of 1300° and 2500° F.),the product of C₂ H₄ is favored. This means that the reaction must bequenched rapidly. When solids are used, they must be separated from thegas rapidly or quenched with the gas. If the gases and solids are notseparated rapidly (but separated) as in a cyclone, and then quenched,product degradation will occur. If the total mix is quenched, to avoidrapid separation, a high thermal inefficiency will result since all theheat of the solids will be rejected to some lower level heat recovery.Hence, a rapid high efficiency separator is optimal for a TRC process.

SUMMARY OF INVENTION

It is an object of the separator of this invention to obtain a primaryseparation of particulate solids from a mixed phase gas-solid stream, asparticularly adapted for use in a TRC system.

It is also an object of the separator to effect the separation rapidlyand with a minimum of erosion.

An additional object of this invention is to provide a separation systemthat obtains essentially complete separation of gas from the solidsphase, although a controlled flow of gas with the solids phase isconsistent with the operation of the device.

Another object of this invention is to provide a separation system toafford essentially complete separation of solids from the mixed phasestream.

A further object is to effect a separation at high temperature and/orhigh velocity conditions with a minimum of gas product degradation.

Another object of this invention is to provide a method for rapidlyattaining a primary separation of solids from a mixed phase gas-solidstream.

These and other objects of this invention will be apparent from aninspection of the specification and figures and claims.

The separation device and system of the present invention as embodied ina TRC system having a low residence time, rapidly disengages particulatesolids from a mixed phase gas-solids stream with a minimum of erosion.The separator consists of a chamber having an inlet at one end and asolids outlet at the other with the gas outlet therebetween. Each inletand outlet is normal to the basic flow pattern within the separator. Thegas outlet is oriented so that the gas portion of the feed undergoes a180° change in direction, while the solids outlet is preferably alignedfor downflow. Solids are projected by centrifugal force to a wall of theseparator normal to and opposite to the inlet as the gas changesdirection 180° forming thereat a bed of solids having an arcuate surfaceconfiguration of approximately 90° upon which subsequent solids impinge.The curve of the bed extends to the solids outlet and forms a path alongwhich solids flow. Erosion of the wall opposite the inlet of theseparator is diminished or eliminated by formation of the bed, whichalso aids in establishing a U-shaped 180° flow pattern of the gasstream.

The separation system is comprised of the primary separator, a secondaryseparator, and a stripping vessel. The gas outlet of the primaryseparator is connected to the secondary separator via a conduit, whilethe stripping vessel is similarly connected to the solids outlet.Pressure regulating means are used to control the flow of gas to thestripping vessel.

In the preferred separator embodiment a weir is used to establish a morestable bed, although a separator may be used without a weir.Alternatively, the solids outlet flow path may be restricted by othermeans which aid in the deaeration of solids. However, in all embodimentsof the separator of the present invention the loss of gas entrained withthe solids phase is small because of the directional changes imposed onboth gas and solid phases.

In the preferred embodiment the separator is designed within severalgeometric constraints in order to maximize the separation efficiency. Itis essential that the flow path have a rectangular cross section inorder to obtain good efficiency. To obtain high efficiencies a separatorwith an inlet inside diameter D_(i) should preferably have a flow pathheight of at least D_(i) or 4 inches, whichever is greater. Similarly,the width of the flow path should be between 0.75 and 1.25 D_(i) whilethe distance between inlet and gas outlet centerlines should be nogreater than 4 times D_(i).

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a TRC system and process according tothe prior art.

FIG. 2 is a schematic flow diagram of the separation system of thepresent invention as appended to a typical tubular reactor.

FIG. 3 is a cross sectional elevational view of the preferred embodimentof the separator.

FIG. 4 is a cutaway view through section 4--4 of FIG. 3.

FIG. 5 is a cutaway view of FIG. 3 showing an alternate geometricconfiguration of the separator shell.

FIG. 6 is a sketch of the separation device of the present inventionindicating gas and solids phase flow patterns in a separator without aweir.

FIG. 7 is a sketch of an alternate embodiment of the separation devicehaving a weir and an extended separation chamber.

FIG. 8 is a sketch of an alternate embodiment of the separation devicewherein a stepped solids outlet is employed, said outlet having asection collinear with the flow path as well as a gravity flow section.

FIG. 9 is a variation of the embodiment of FIG. 8 in which the solidsoutlet of FIG. 7 is used, but is not stepped.

FIG. 10 is a sketch of a variation of the separation device of FIG. 8wherein a venturi restriction is incorporated in the collinear sectionof the solids outlet.

FIG. 11 is a variation of the embodiment of FIG. 10 oriented for usewith a riser type reactor.

DESCRIPTION OF INVENTION

FIG. 2 is a schematic flow diagram showing the installation of theseparator system of the present invention in a typical TRC tubularreactor system handling dilute phase solid-gas mixtures. The prior artTRC system is illustrated in FIG. 1 and provides that thermal crackerfeed oil or residual oil, with or without blended distillate heavy gas,enters the system through line 10 and hydrogen enters the system throughline 12. Together the feed oil and hydrogen pass throughhydrodesulfurized zone 14. Hydrodesulfurization effluent passes throughline 16 and enters flash chamber 18 from which hydrogen andcontaminating gases including hydrogen sulfide and ammonia are removedoverhead through line 20, while flash liquid is removed through line 22.The flash liquid passes through preheater 24, is admixed with dilutionsteam entering through line 26 and then flows to the bottom of thermalcracking reactor 28 through line 30.

A stream of hot regenerated solids is charged through line 32 andadmixed with steam or other fluidizing gas entering through line 34prior to entering the bottom of riser 28. The oil, steam and hot solidspass in entrained flow upwardly through riser 28 and are dischargedthrough a curved segment 36 at the top of the riser to inducecentrifugal separation of solids from the effluent stream. A streamcontaining most of the solids passes through riser discharge segment 38and can be mixed, if desired, with make-up solids entering through line40 before or after entering solids separator-stripper 42. Another streamcontaining most of the cracked product is discharged axially throughconduit 44 and can be cooled by means of a quench stream enteringthrough line 46 in advance of solids separator-stripper 48.

Stripper steam is charged to solids separators 42 and 48 through lines50 and 52, respectively. Product streams are removed from solidsseparators 42 and 48 through lines 54 and 56, respectively, and thencombined in line 58 for passage to a secondary quench and productrecovery train, not shown. Coke-laden solids are removed from solidsseparators 42 and 48 through lines 60 and 62, respectively, and combinedin line 64 for passage to coke burner 66. If required, torch oil can beadded to burner 66 through line 68 while stripping steam may be addedthrough line 70 to strip combustion gases from the heated solids. Air ischarged to the burner through line 69. Combustion gases are removed fromthe burner through line 72 for passage to heat and energy recoverysystems, not shown, while regenerated hot solids which are relativelyfree of coke are removed from the burner through line 32 for recycle toriser 28. In order to produce a cracked product containing ethylene andmolecular hydrogen, petroleum residual oil is passed through thecatalytic hydrodesulfurization zone in the presence of hydrogen at atemperature between 650° F. and 900° F., with the hydrogen beingchemically combined with the oil during the hydrocycling step. Thehydrodesulfurized residual oil passes through the thermal cracking zonetogether with the entrained inert hot solids functioning as the heatsource and a diluent gas at a temperature between about 1300° F. and2500° F. for a residence time between about 0.05 to 2 seconds to producethe cracked product, such as ethylene, and hydrogen. For the productionof ethylene by thermally cracking a hydrogen feed at least 90 volumepercent of which comprises a light gas oil fraction of a crude oilboiling between 400° F. and 650° F., the hydrocarbon feed, along withdiluent gas and entrained inert hot gases are passed through thecracking zone at a temperature between 1300° F. and 2500° F. for aresidence time of 0.05 to 2 seconds. The weight ratio of gas oil to fueloil is at least 0.3, while the cracking severity corresponds to amethane yield of at least 12 weight percent based on said feed oil.Quench cooling of the product immediately upon leaving the cracked zoneto a temperature below 1300° F. ensures that the ethylene yield isgreater than the methane yield on a weight basis.

Referring to FIG. 2 in the subject invention, in lieu of a separationzone or curved segment region 36 and the quench area 44 of the prior artTRC system (see FIG. 1), solids and gas enter the tubular reactor 13Dthrough lines 11D and 12D respectively. The reactor effluent flowsdirectly to separator 14D where a separation into a gas phase and asolids phase stream is effected. The gas phase is removed via line 15D,while the solid phase is sent to the stripping vessel 22D via line 16D.Depending upon the nature of the process and the degree of separation,an in-line quench of the gas leaving the separator via line 15D may bemade by injecting quench material from line 17D. Usually, the productgas contains residual solids and is sent to a secondary separator 18D,preferably a conventional cyclone. Quench material should be introducedin line 15D in a way that precludes back flow of quench material to theseparator. The residual solids are removed from separator 18D via line21D, while essentially solids free product gas is removed overheadthrough line 19D. Solids from lines 16D and 21D are stripped of gasimpurities in fluidized bed stripping vessel 22D using steam or otherinert fluidizing gas admitted via line 23D. Vapors are removed from thestripping vessel through line 24D and, if economical or if need be, sentto down-stream purification units. Stripped solids removed from thevessel 22D through line 25D are sent to regeneration vessel 27D usingpneumatic transport gas from line 26D. Off gases are removed from theregenerator through line 28D. After regeneration the solids are thenrecycled to reactor 13D via line 11D.

The separator 14D should disengage solids rapidly from the reactoreffluent in order to prevent product degradation and ensure optimalyield and selectivity of the desired products. Further, the separator14D operates in a manner that eliminates or at least significantlyreduces the amount of gas entering the stripping vessel 22D inasmuch asthis portion of the gas product would be severely degraded by remainingin intimate contact with the solid phase. This is accomplished with apositive seal which has been provided between the separator 14D and thestripping vessel 22D. Finally, the separator 14D operates so thaterosion is minimized despite high temperature and high velocityconditions that are inherent in many of these processes. The separatorsystem of the present invention is designed to meet each one of thesecriteria as is described below.

FIG. 3 is a cross sectional elevational view showing the preferredembodiment of solids-gas separation device 14D of the present invention.The separator 14D is provided with a separator shell 37D and iscomprised of a solids-gas disengaging chamber 31D having an inlet 32Dfor the mixed phase stream, a gas phase outlet 33D, and a solids phaseoutlet 34D. The inlet 32D and the solids outlet 34D are preferablylocated at opposite ends of the chamber 31D. While the gas outlet 33Dlies at a point therebetween. Clean-out and maintenance manways 35D and36D may be provided at either end of the chamber 31D. The separatorshell 37D and manways 35D and 36D preferably are lined with erosionresistent linings 38D, 39D and 41D respectively which may be required ifsolids at high velocities are encountered. Typical commerciallyavailable materials for erosion resistent lining include CarborundumPrecast Carbofrax D, Carborundum Precast Alfrax 201 or their equivalent.A thermal insulation lining 40D may be placed between shell 37D andlining 38D and between the manways and their respective erosionresistent linings when the separator is to be used in high temperatureservice. Thus, process temperatures above 1500° F. (870° C.) are notinconsistent with the utilization of this device.

FIG. 4 shows a cutaway view of the separator along section 4--4. Forgreater strength and ease of construction the separator 14D shell ispreferably fabricated from cylindrical sections such as pipe 50D,although other materials may, of course, be used. It is essential thatlongitudinal side walls 51D and 52D should be rectilinear, or slightlyarcuate as indicated by the dotted lines 51aD and 52aD. Thus, flow path31AD through the separator is essentially rectangular in cross sectionhaving a height H and width W as shown in FIG. 4. The embodiment shownin FIG. 4 defines the geometry of the flow path by adjustment of thelining width for walls 51D and 52D. Alternatively, baffles, inserts,weirs or other means may be used. In like fashion the configuration ofwalls 53D and 54D transverse to the flow path may be similarly shaped,although this is not essential. FIG. 5 is a cutaway view of FIG. 3wherein the separation shell 37D is fabricated from a rectangularconduit. Because the shell 37D has rectilinear walls 51D and 52D it isnot necessary to adjust the width of the flow path with a thickness oflining. Linings 38D and 40D could be added for erosion and thermalresistence respectively.

Again referring to FIG. 3, inlet 32D and outlet 33D are disposed normalto flow path 31D (shown in FIG. 4) so that the incoming mixed phasestream from inlet 32D is required to undergo a 90° change in directionupon entering the chamber. As a further requirement, however, the gasphase outlet 33D is also oriented so that the gas phase upon leaving theseparator has completed a 180° change in direction.

Centrifugal force propels the solid particles to the wall 54D oppositeinlet 32D of the chamber 31D, while the gas portion, having lessmomentum, flows through the vapor space of the chamber 31D. Initially,solids impinge on the wall 54D, but subsequently accumulate to form astatic bed of solids 42D, which ultimately forms in a surfaceconfiguration having a curvilinear arc 43D of approximately 90°. Solidsimpinging upon the bed are moved along the curvilinear arc 43D to thesolids outlet 34D which is preferably oriented for downflow of solids bygravity. The exact shape of the arc 43D is determined by the geometry ofthe particular separator and the inlet stream parameters such asvelocity, mass flowrate, bulk density, and particle size. Because theforce imparted to the incoming solids is directed against the static bed42D rather than the separator 14D itself, erosion is minimal. Separatorefficiency, defined as the removal of solids from the gas phase leavingthrough outlet 33D, is, therefore, not affected adversely by high inletvelocities, up to 150 ft./sec., and the separator 14D is operable over awide range of dilute phase densities, preferably between 0.1 and 10.0lbs./ft³. The separator 14D of the present invention achievesefficiencies of about 80%, although the preferred embodiment, discussedbelow, can obtain over 90% removal of solids.

It has been found that separator efficiency is dependent upon separatorgeometry inasmuch as the flow path must be essentially rectangular andthe relationship between height H, and the sharpness of the U-bend inthe gas flows is significant.

Referring to FIGS. 3 and 4 we have found that for a given height H ofchamber 31D, efficiency increases as the 180° U-bend between inlet 32Dand outlet 33D becomes progressively sharper; that is, as outlet 33D isbrought progressively closer to inlet 32D. Thus, for a given H theefficiency of the separator increases as the flow path and, hence,residence time decreases. Assuming an inside diameter D_(i) of inlet32D, the preferred distance CL between the centerlines of inlet 32D andoutlet 33D is less than 4.0 D_(i), while the most preferred distancebetween said centerlines is between 1.5 and 2.5 D₁. Below 1.5 D_(i)better separation is obtained but difficulty in fabrication makes thisembodiment less attractive in most instances. Should this latterembodiment be desired, the separator 14D would probably require aunitary casting design because inlet 32D and outlet 33D would be tooclose to one another to allow welded fabrication.

It has been found that the height of flow path H should be at leastequal to the value of D_(i) or 4 inches in height, whichever is greater.Practice teaches that if H is less than D_(i) or 4 inches the incomingstream is apt to disturb the solids in the bed 42D, therebyre-entraining solids in the gas product leaving through outlet 33D.Preferably H is on the order of twice D_(i) to obtain even greaterseparation efficiency. While not otherwise limited, it is apparent thattoo large an H eventually merely increases residence time withoutsubstantive increases in efficiency. The width W of the flow path ispreferably between 0.75 and 1.25 times D_(i), most preferably between0.9 and 1.10 D_(i).

Outlet 33D may be of any inside diameter. However, velocities greaterthan 75 ft./sec. can cause erosion because of residual solids entrainedin the gas. The inside diameter of outlet 34D should be sized so that apressure differential between the stripping vessel 22D shown in FIG. 2and the separator 14D exist such that a static height of solids isformed in solids outlet line 16D. The static height of solids in line16D forms a positive seal which prevents gases from entering thestripping vessel 22D. The magnitude of the pressure differential betweenthe stripping vessel 22D and the separator 14D is determined by theforce required to move the solids in bulk flow to the solids outlet 34Das well as the height of solids in line 16D. As the differentialincreases the net flow of gas to the stripping vessel 22D decreases.Solids, having gravitational momentum, overcome the differential, whilegas preferentially leaves through the gas outlet 33D.

By regulating the pressure in the stripping vessel 22D it is possible tocontrol the amount of gas going to the stripper. The pressure regulatingmeans may include a check or "flapper" valve 29D at the outlet of line16D, or a pressure control valve 29aD in line 24D. Alternatively, assuggested above, the pressure may be regulated by selecting the size ofthe outlet 34D and conduit 16D to obtain hydraulic forces acting on thesystem that set the flow of gas to the stripper 32D. While such gas isdegraded, we have found that an increase in separation efficiency occurswith a bleed of gas to the stripper of less than 10%, preferably between2 and 7%. Economic and process considerations would dictate whether thismode of operation should be used. It is also possible to design thesystem to obtain a net backflow of gas from the stripping vessel. Thisgas flow should be less than 10% of the total feed gas rate.

By establishing a minimal flow path, consistent with the aboverecommendations, residence times as low as 0.1 seconds or less may beobtained, even in separators having inlets over 3 feet in diameter.Scale-up to 6 feet in diameter is possible in many systems whereresidence times approaching 0.5 seconds are allowable.

In the preferred embodiment of FIG. 3, a weir 44D is placed across theflow path at a point at or just beyond the gas outlet to establish apositive height of solids prior to solids outlet 34D. By installing aweir (or an equivalent restriction) at this point a more stable bed isestablished thereby reducing turbulence and erosion. Moreover, the weir44D establishes a bed which has a crescent shaped curvilinear arc 43D ofslightly more than 90°. An arc of this shape diverts gas towards the gasoutlet and creates the U-shaped gas flow pattern illustrateddiagrammatically by line 45D in FIG. 3. Without the weir 44D an arcsomewhat less than or equal to 90° would be formed, and which wouldextend asymptotically toward outlet 34D as shown by dotted line 60D inthe schematic diagram of the separator of FIG. 6. While neitherefficiency nor gas loss (to the stripping vessel) is affected adversely,the flow pattern of line 61D increases residence time, and moreimportantly, creates greater potential for erosion at areas 62D, 63D and64D.

The separator of FIG. 7 is a schematic diagram of another embodiment ofthe separator 14D, said separator 14D having an extended separationchamber in the longitudinal dimension. Here, the horizontal distance Lbetween the gas outlet 33D and the weir 44D is extended to establish asolids bed of greater length. L is preferably less than or equal to 5D_(i). Although the gas flow pattern 61D does not develope the preferredU-shape, a crescent shaped arc is obtained which limits erosionpotential to area 64D. Embodiments shown by FIGS. 6 and 7 are usefulwhen the solids loading of the incoming stream is low. The embodiment ofFIG. 6 also has the minimum pressure loss and may be used when thevelocity of the incoming stream is low.

As shown in FIG. 8 it is equally possible to use a stepped solids outlet65D having a section 66D collinear with the flow path as well as agravity flow section 67D. Wall 68D replaces weir 44D, and arc 43D andflow pattern 45D are similar to the preferred embodiment of FIG. 3.Because solids accumulate in the restricted collinear section 66D,pressure losses are greater. This embodiment, then, is not preferredwhere the incoming stream is at low velocity and cannot supplysufficient force to expel the solids through outlet 65D. However,because of the restricted solids flow path, better deaeration isobtained and gas losses are minimal.

FIG. 9 illustrates another embodiment of the separator 14D of FIG. 8wherein the solids outlet is stepped. Although a weir is not used, theoutlet restricts solids flow which helps form the bed 42D. As in FIG. 7,an extended L distance between the gas outlet and solids outlet may beused.

The separator of FIG. 8 or 9 may be used in conjunction with a venturi,an orifice, or an equivalent flow restriction device as shown in FIG.10. The venturi 69D having dimensions D_(v) (diameter at venturi inlet),D_(vt) (diameter of venturi throat), and θ (angle of cone formed byprojection of convergent venturi walls) is placed in the collinearsection 66D of the outlet 65D to greatly improve deaeration of solids.The embodiment of FIG. 11 is a variation of the separator shown in FIG.10. Here, inlet 32 and outlet 33D are oriented for use in a riser typereactor. Solids are propelled to the wall 71D and the bed thus formed iskept in place by the force of the incoming stream. As before the gasportion of the feed follows the U-shaped pattern of line 45D. However,an asymptotic bed will be formed unless there is a restriction in thesolids outlet. A weir would be ineffective in establishing bed height,and would deflect solids into the gas outlet. For this reason the solidsoutlet of FIG. 10 is preferred. Most preferably, the venturi 69D isplaced in collinear section 66D as shown in FIG. 11 to improve thedeaeration of the solid. Of course, each of these alternate embodimentsmay have one or more of the optional design features of the basicseparator discussed in relation to FIGS. 3, 4 and 5.

The separator of the present invention is more clearly illustrated andexplained by the examples which follow. In these examples, which arebased on data obtained during experimental testing of the separatordesign, the separator has critical dimensions specified in Table I.These dimensions (in inches except as noted) are indicated in thevarious drawing figures and listed in the Nomenclature below:

                                      TABLE I                                     __________________________________________________________________________    CL         Distance between inlet and gas outlet centerlines                  D.sub.i    Inside diameter of inlet                                           D.sub.og   Inside diameter of gas outlet                                      D.sub.os   Inside diameter of solids outlet                                   D.sub.v    Diameter of venturi inlet                                          D.sub.vt   Diameter of venturi throat                                         H          Height of flow path                                                H.sub.w    Height of weir or step                                             L          Length from gas outlet to weir or step as                                     indicated in FIG. 7                                                W          Width of flow path                                                 θ    Angle of cone formed by projection                                            of convergent venturi walls, degrees                               Dimensions of Separators in Examples 1 to 10, in inches*                      Examples                                                                      Dimension                                                                           1  2  3  4  5  6  7  8  9 10                                            __________________________________________________________________________    CL    3.875                                                                            3.875                                                                            3.875                                                                            5.875                                                                            5.875                                                                            5.875                                                                            11 11 3.5                                                                             3.5                                           D.sub.i                                                                             2  2  2  2  2  2  6  6  2 2                                             D.sub.og                                                                            1.75                                                                             1.75                                                                             1.75                                                                             1.75                                                                             1.75                                                                             1.75                                                                             4  4  1 1                                             D.sub.os                                                                            2  2  2  2  2  2  6  6  2 2                                             D.sub.v                                                                             -- -- -- -- -- -- -- -- --                                                                              2                                             D.sub.vt                                                                            -- -- -- -- -- -- -- -- --                                                                              1                                             H     4  4  4  4  4  4  12 12 7.5                                                                             6.75                                          H.sub.w                                                                             0.75                                                                             0.75                                                                             0.75                                                                             0.75                                                                             0.75                                                                             0.75                                                                             2.25                                                                             2.25                                                                             0 4.75                                          L     0  2  2  0  0  0  0  0  10                                                                              0                                             W     2  2  2  2  2  2  6  6  2 2                                             θ, degrees                                                                    -- -- -- -- -- -- -- -- --                                                                              28.1°                                  __________________________________________________________________________     *Except as noted                                                         

EXAMPLE 1

In this example a separator of the preferred embodiment of FIG. 3 wastested on a feed mixture of air and silica alumina. The dimensions ofthe apparatus are specified in Table I. Note that the distance L fromthe gas outlet to the weir was zero.

The inlet stream was comprised of 85 ft.³ /min. of air and 52 lbs./min.of silica alumina having a bulk density of 70 lbs./ft³ and an averageparticle size of 100 microns. The stream density was 0.612 lbs./ft.³ andthe operation was performed at ambient temperature and atmosphericpressure. The velocity of the incoming stream through the 2 inch inletwas 65.5 ft./sec., while the outlet gas velocity was 85.6 ft./sec.through a 1.75 inch diameter outlet. A positive seal of solids in thesolids outlet prevented gas from being entrained in the solids leavingthe separator. Bed solids were stabilized by placing a 0.75 inch weiracross the flow path.

The observed separation efficiency was 89.1%, and was accomplished in agas phase residence time of approximately 0.008 seconds. Efficiency isdefined as the percent removal of solids from the inlet stream.

EXAMPLE 2

The gas-solids mixture of Example 1 was processed in a separator havinga configuration illustrated by FIG. 7. In the example the L dimension is2 inches; all other dimensions are the same as Example 1. By extendingthe separation chamber along its longitudinal dimension, the flowpattern of the gas began to deviate from the U-shape discussed above. Asa result residence time was longer and turbulence was increased.Separation efficiency for this example was 70.8%.

EXAMPLE 3

The separator of Example 2 was tested with an inlet stream comprised of85 ft.³ /min. of air and 102 lbs./min. of silica alumina which gave astream density of 1.18 lbs./ft.³, or approximately twice that of Example2. Separation efficiency improved to 83.8%.

EXAMPLE 4

The preferred separator of Example 1 was tested at the inlet flow rateof Example 3. Efficiency increased slightly to 91.3%.

EXAMPLE 5

The separator of FIG. 3 was tested at the conditions of Example 1.Although the separation dimensions are specified in Table I note thatthe distance CL between inlet and gas outlet centerlines was 5.875inches, or about three times the diameter of the inlet. This dimensionis outside the most preferred range for CL which is between 1.50 and2.50 Di. Residence time increased to 0.01 seconds, while efficiency was73.0%.

EXAMPLE 6

Same conditions apply as for Example 5 except that the solids loadingwas increased to 102 lbs./min. to give a stream density of 1.18lbs./ft.³. As observed previously in Examples 3 and 4, the separatorefficiency increased with higher solids loading to 90.6%.

EXAMPLE 7

The preferred separator configuration of FIG. 3 was tested in thisExample. However, in this example the apparatus was increased in sizeover the previous examples by a factor of nine based on flow area. A 6inch inlet and 4 inch outlet were used to process 472 ft.³ /min. of airand 661 lbs./min. of silica alumina at 180° F. and 12 psig. Therespective velocities were 40 and 90 ft./sec. The solids had a bulkdensity of 70 lbs./ft³ and the stream density was 1.37 lbs./ft.³Distance CL between inlet and gas outlet centerlines was 11 inches, or1.83 times the inlet diameter; distance L was zero. The bed wasstabilized by a 2.25 inch weir, and gas loss was prevented by a positiveseal of solids. However, the solids were collected in a closed vessel,and the pressure differential was such that a positive flow of displacedgas from the collection vessel to the separator was observed. Thisvolume was approximately 9.4 ft.³ /min. Observed separator efficiencywas 90.0%, and the gas phase residence time was approximately 0.02seconds.

EXAMPLE 8

The separator used in Example 7 was tested with an identical feed of gasand solids. However, the solids collection vessel was vented to theatmosphere and the pressure differential adjusted such that 9% of thefeed gas, or 42.5 ft.³ /min. exited through the solids outlet at avelocity of 3.6 ft./sec. Separator efficiency increased with thispositive bleed through the solids outlet to 98.1%.

EXAMPLE 9

The separator of FIG. 9 was tested in a unit having a 2 inch inlet and a1 inch gas outlet. The solids outlet was 2 inches in diameter and waslocated 10 inches away from the gas outlet (dimension L). A weir was notused. The feed was comprised of 85 ft.³ /min. of air and 105 lbs./min.of spent fluid catalytic cracker catalyst having a bulk density of 45lbs./ft.³ and an average particle size of 50 microns. This gave a streamdensity of 1.20 lbs./ft.³ Gas inlet velocity was 65 ft./sec. while thegas outlet velocity was 262 ft./sec. As in Example 7 there was apositive counter-current flow of displaced gas from the collectionvessel to the separator. This flow was approximately 1.7 ft.³ /min. at avelocity of 1.3 ft./sec. Operation was at ambient temperature andatmospheric pressure. Separator efficiency was 95.0%.

EXAMPLE 10

The separator of FIG. 10 was tested on a feed comprised of 85 ft.³ /min.of air and 78 lbs./min. of spent Fluid Catalytic Cracking catalyst. Theinlet was 2 inches in diameter which resulted in a velocity of 65ft./sec., the gas outlet was 1 inch in diameter which resulted in anoutlet velocity of 262 ft./sec. This separator had a stepped solidsoutlet with a venturi in the collinear section of the outlet. Theventuri mouth was 2 inches in diameter, while the throat was 1 inch. Acone of 28.1° was formed by projection of the convergent walls of theventuri. An observed efficiency of 92.6% was measured, and the solidsleaving the separator were completely deaerated except for interstitialgas remaining in the solid's voids.

We claim:
 1. In a TRC apparatus having a tubular thermal crackingreactor including a reaction chamber cracking zone, means for deliveringhot inert particulate solids to the reactor, means for deliveringhydrocarbon feed or hydrodesulfurized residual oil fluid feed to thereactor and means for delivering a diluent gas at a temperature between1300° F. and 2500° F. to the reactor and wherein the hydrocarbon fluidfeed or the hydrodesulfurized residual oil fluid feed along with theinert particulate solids and diluent gas are passed through the crackingzone for a residence time of 0.05 to 2 seconds, the improvementcomprising a solids-gas separator designed to effect rapid removal ofparticulate solids from a dilute mixed phase stream of solids and gasleaving the reactor, said separator comprising a chamber for disengagingsolids from the incoming mixed phase stream, said chamber havingrectilinear longitudinal walls to form a flow path essentiallyrectangular in cross section, said chamber also having a mixed phaseinlet, a gas phase outlet, and a solids phase outlet, with the inletbeing at one end of the chamber disposed normal to one wall of therectilinear chamber, the solids phase outlet being at the other end ofthe chamber and suitably arranged for downflow of discharged solids bygravity, and the gas outlet being therebetween and oriented to effect a180° change in direction of the gas and wherein the separator furthercomprises a weir disposed in said chamber and extending across the flowpath adjacent the gas phase outlet upstream of the solids phase outlet.2. In a TRC apparatus having a tubular thermal cracking reactorincluding a reaction zone, means for delivering hot inert particulatesolids to the reactor, means for delivering hydrocarbon feed orhydrodesulfurized residual oil fluid feed to the reactor and means fordelivering a diluent gas at a temperature between 1300° F. and 2500° F.to the reactor and wherein the hydrocarbon fluid feed or thehydrodesulfurized residual oil fluid feed along with the hot inertparticulate solids and diluent gas are passed through the reaction zonefor a residence time of 0.05 to 2 seconds, the improvement comprising asolids-gas separator designed to effect rapid removal of particulatesolids from a dilute mixed phase stream of solids and gas leaving thereactor, the separator comprising a chamber for disengaging solids fromthe incoming mixed phase stream, said chamber having slightly arcuatelongitudinal walls to form a flow path essentially rectangular in crosssection, said chamber also having a mixed phase inlet, a gas phaseoutlet, and a solids phase outlet, with the mixed phase inlet being atone end of the chamber and disposed normal to one wall of therectilinear chamber, and the solids phase outlet being at the other endof the chamber and suitably arranged for downflow of discharged solidsby gravity, and said gas phase outlet being therebetween and oriented toeffect a 180° change in direction of the gas, and wherein said separatorfurther comprises a weir disposed in said chamber and extending acrosssaid flow path adjacent said gas phase outlet upstream of said solidsphase outlet.
 3. In a TRC apparatus as in claim 1 or 2, wherein theseparator mixed phase inlet is of an inside diameter D_(i), and whichseparator is further characterized by the flow path having a preferredheight H equal to at least D_(i) or 4 inches, whichever is greater, andwith a preferred width W between 0.75 and 1.25 D_(i), and wherein thegas phase outlet is located between the mixed phase inlet and the solidsphase outlet at a preferred distance from the mixed phase inlet which isno greater than 4.0 D_(i) as measured between their respectivecenterlines.
 4. In a TRC apparatus as in claim 3 wherein the distancebetween inlet and gas outlet centerlines of the separator is no lessthan 1.5 D_(i) but not greater than 2.5 D_(i).
 5. In a TRC apparatus asin claim 4 wherein the height H of the flow path in the separator istwice D_(i).
 6. In a TRC apparatus as in claim 5 wherein the width W ofthe flow path in the separator is no less than 0.9 D_(i) but no greaterthan 1.10 D_(i).
 7. The TRC apparatus of claim 3 wherein the chamber inthe separator has a longitudinal dimension that is extended beyond thegas outlet by a length L.
 8. The TRC apparatus as in claim 7 wherein thelength L of the chamber extension in the separator is less than or equalto 5 D_(i).
 9. In a TRC apparatus having a tubular thermal crackingreactor including a reaction chamber, means for delivering hot inertparticulate solids to the reactor, means for delivering hydrocarbon feedor hydrodesulfurized residual oil fluid feed to the reactor and meansfor delivering a diluent gas at a temperature between 1300° F. and 2500°F. to the reactor and wherein the hydrocarbon feed or thehydrodesulfurized residual oil fluid feed along with the inertparticulate solids and diluent gas are passed through the reactionchamber for a residence time of 0.05 to 2 seconds, the improvementcomprising:a solids-gas separation system to separate a dilute mixedphase stream of gas and particulate solids leaving the reactor into anessentially solids free gas stream, the separation system comprising: achamber for rapidly disengaging about 80% of the particulate solids fromthe incoming dilute mixed phase stream, said chamber havingapproximately rectilinear or slightly arcuate longitudinal side walls toform a flow path of height H and width W approximately rectangular incross section, said chamber also having a mixed phase inlet of insidewidth D_(i), a gas outlet, and a solids outlet, said inlet being at oneend of the chamber and disposed normal to the flow path the height H ofwhich is equal to at least D_(i) or 4 inches, whichever is greater, andthe width W of which is no less than 0.75 D_(i) but no more than 1.25D_(i), said solids outlet being at the opposite end of the chamber andbeing suitably arranged for downflow of discharged solids by gravity,and said gas outlet being therebetween at a distance no greater than 4D_(i) from the inlet as measured between respective centerlines andoriented to effect a 180° change in direction of the gas wherebyresultant centrifugal forces direct the solid particles in the incomingstream toward a wall of the chamber opposite to the inlet formingthereat and maintaining an essentially static bed of solids, the surfaceof the bed defining a curvilinear path of an arc of approximately 90° ofa circle for the outflow of solids to the solids outlet, a secondarysolids-gas separator, said secondary separator removing essentially allof the residual solids, a first conduit connecting the gas outlet fromthe chamber to the secondary separator, a vessel connected to saidsolids outlet for the discharge of solids, a second conduit connectingsaid vessel to the solids outlet and, pressure balance means to maintaina height of solids in said second conduit to provide a positive sealbetween the chamber and vessel.
 10. The TRC apparatus of claim 9 whereinthe pressure balance means is the hydraulic forces acting on thechamber, second conduit and vessel, the second conduit being sized forsufficient pressure loss to provide the height of solids.
 11. The TRCapparatus of claim 9 wherein the pressure balance means is a check valveat the outlet end of the second conduit.
 12. The TRC apparatus of claim9 wherein the pressure balance means is a pressure control valve on thesolids discharge vessel.